Electrostatic gas cleaning

ABSTRACT

Suspended matter is removed from combustion gases containing sulfur dioxide by removing a major portion of the particulate matter from a minor portion of the gases, catalytically converting a major portion of the sulfur dioxide content of said minor portion of the gases to sulfur trioxide, mixing said minor portion of the gases with the main gas stream and subjecting the mixed gases to electrical precipitation.

United States Patent [72] Inventor Lawrence M. Roberts Bound Brook, NJ.211 Appl. No. 678,300 [22] Filed Oct. 26, 1967 [45] Patented June 1,1971 [73] Assignee Research-CottrelLlnc. Somerset County, NJ.

[541 ELECTROSTATIC GAS CLEANING 3 Claims, 1 Drawing Fig.

[52] U.S.Cl. 55/4, 23/2, 23/175, 55/5,55/11, 55/106, 55/128, 55/135, 55/136 [51] Int. Cl B03c 3/01 [50] Field oiSearch 55/2, 5,11,101,122,134,135,4,106,128,136;23/2, 2.2, 174, 175

[56] References Cited UNlTED STATES PATENTS 334,158 l/1886 Beard 55/220X1,291,745 l/l9l9 Bradley 55/5 2,180,727 11/1939 Carter 23/175 2,537,5581/1951 Tigges 55/124X 2,696,892 12/1954 Campbell 55/122X 2,706,5334/1955 Hedberg et a1. 55/135X 2,740,493 4/ 1956 Wintermute 55/127X2,746,563 5/1956 Harlow 23/175X 2,758,666 8/ 1956 Prentiss 55/124X2,795,401 6/1957 Cooper et a1. 55/135X 2,841,242 7/1958 Hall 23/174X3,054,243 9/ 1962 Howe 55/1 1 3,132,473 S/1964 Hass 60/29 all- OTHERREFERENCES White, Harry J., industrial Electrostatic Precipitation,Addison-Wesley Publishing Company, 1nc., Reading, Massachusetts, 1963,pages 294, 295, and 303- 305 (copy in Technical Library, Call No. TP 156p7w5i) Primary Examiner-Dennis E. Talbert, Jr. Attorney-Stowell &Stowell ABSTRACT: Suspended matter is removed from combustion gasescontaining sulfur dioxide by removing a major portion of the particulatematter from a minor portion of the gases, catalytically converting amajor portion of the sulfur dioxide content of said minor portion of thegases to sulfur trioxide, mixing said minor portion of the gases withthe main gas stream and subjecting the mixed gases to electricalprecipitation.

PATENTEU JUN 1 I971 3,581,463

INVENTUR LAWRENCE. M ROBERTS ATTURNHY ELECTROSTATIC GAS CLEANING Thisinvention relates to the removal of suspended particulate matter fromcombustion gases containing sulfur dioxide by subjecting the gases toelectrical precipitation in a high potential electrostatic field.

Difficulty has been encountered in the electrical precipitation ofsuspended particles or fly ash from combustion gases arising from thephenomenon of back discharge due to high resistivity of the particulatematerial and it has been proposed to overcome this difficulty bycatalytically converting sulfur dioxide in the gases to sulfur trioxideto increase the conductivity of the particulate material in the gases.However, the catalyst rapidly loses its efficiency and the catalyst bedrapidly increases its resistance to the flow of gases therethrough dueto the accumulation of particulate matter thereon.

Since combustion gases typically contain a much larger amount of sulfurdioxide than is required to produce the amount of sulfur trioxidedesired for effective conditioning of the particulate material forefficient electrical precipitation, it has been found that thesedifficulties may be avoided by sub jecting only a minor portion of thegases to catalytic sulfur dioxide conversion after removing from suchminor portion of the gases a major portion of their suspendedparticulate matter preferably by electrical precipitation at a high tem'perature, for example, from about 800 to about l,000 F. This minorportion of the gas is then mixed with the main gas stream either beforeor after it has been cooled, for example, in a combustion air preheater,and the mixed gases are subjected to a conventional electricalprecipitation operation.

In a typical powdered coal boiler installation the sulfur dioxidecontent of the combustion gases coming from the boiler would be about0.1 percent by volume whereas conversion of from 0.001 percent to 0.005percent of sulfur dioxide by volume to sulfur trioxide would beeffective to adequately condition the gases for efficient electricalprecipitation of the fly ash. Thus the auxiliary gas cleaner andcatalyst chamber needed for the method of the invention would only haveto be large enough, in this case, to handle from 1 percent to 5 percentby volume of the combustion gases.

The invention will be more particularly described with reference to theaccompanying drawing showing diagrammatically an illustrative form ofapparatus embodying the principles of the invention.

In the drawing is the main flue leading from the combustion chamber ofacoal fired boiler (not shown) through air preheater ll, electricalprecipitator l2 and fan 13 to a chimney stack (not shown). An auxiliaryfan 14 draws a small portion of the gases from the main flue and passesthem successively through high temperature electrical precipitator l5and catalyst chamber 16 back to the main flue upstream of the mainprecipitator I2.

In a typical operation, 2 percent of the combustion gases coming fromthe boiler at about 800 F. and containing about 0.l percent by volume ofsulfur dioxide are passed by fan 14 through electrostatic cleaner 15through catalyst chamber 16, where substantially all of the sulfurdioxide is converted to sulfur trioxide by catalyst 17 which may be, forexample, a vanadium pentoxide catalyst on silica gel granules or any ofthe commercially available sulfur dioxide oxidation catalysts. Thesulfur trioxide containing gas is then returned to the main gas streamwhich has been cooled to about 300 F. in heat exchanger 11 and the mixedgases are passed through electrical precipitator l2.

lclaim:

l. A method of removing suspended matter from combustion gasescontaining sulfur dioxide which comprises removing from a minor portionof the gases a major portion of the particulate content thereof,subjecting said minor portion of the gases to the action of a catalystto convert a major portion of the sulfur dioxide content thereof tosulfur trioxide, mixing said minor portion of the gases with the maingas stream and subjecting the mixed gases to electrical precipitation,the amount of sulfur dioxide converted to sulfur trioxide in said minorortion of the as stream being equivalent to from about 0. 01 percent toa out 0.005 percent by volume of the total gas stream coming from theboiler.

2. A method of removing suspended matter from combustion gases asdefined in claim 1 wherein the particulate content is removed from theminor portion of the gas stream at a temperature of from about 800 toabout 1,000 F.

3. A method of removing suspended matter from combustion gases asdefined in claim I wherein the particulate content is removed from theminor portion of the gas stream by electrical precipitation at atemperature of about 800 F. to about l,000 F. and particulate content isremoved from the mixed gases by electrical precipitation at atemperature of about 300 F.

2. A method of removing suspended matter from combustion gases asdefined in claim 1 wherein the particulate content is removed from theminor portion of the gas stream at a temperature of from about 800* toabout 1,000* F.
 3. A method of removing suspended matter from combustiongases as defined in claim 1 wherein the particulate content is removedfrom the minor portion of the gas stream by electrical precipitation ata temperature of about 800* F. to about 1,000* F. and particulatecontent is removed from the mixed gases by electrical precipitation at atemperature of about 300* F.